It would be nice to be able to introduce transformations which are applied to method parameters, like this:

@Message(id = 1234, value = "This is a bad %s")
IllegalStateException badType(@Transform(GET_CLASS) Object thing);

...where GET_CLASS comes from an enum of predefined transformations. The resultant code would replace thing in the final rendering with thing == null ? null : thing.getClass().

It might make sense to support multiple transforms too:

@Message(value = "The class' hash is %x")
String hashWoo(@Transform({GET_CLASS, HASH_CODE}) Object thing);

in which case the transforms would be applied in order from left to right. Some transform ideas:

• GET_CLASS -> x == null ? null : x.getClass()
• HASH_CODE -> x == null ? 0 : x.hashCode()
• IDENTITY_HASH_CODE -> x == null ? 0 : System.identityHashCode( x )
• SIZE -> depending on type, choose String.length(), array.length, Collection/Map.size()

In the generated comments, the parameter descriptions should include the transformations applied (in English order i.e. right to left, opposite of the enum list order on the annotation):

// parameter 1 - thing
// parameter 2 - class of thing
// parameter 3 - hashCode of class of thing